1. Field of the Invention
The present invention relates to electronic navigation maps, and, more particularly, to rendering images for electronic navigation maps.
2. Description of the Related Art
Navigation maps are essential resources for visitors to an unfamiliar city because these maps visually highlight landmarks including buildings, natural features, and points of interest (POIs) such as museums, restaurants, parks and shopping districts. While most in-car and portable navigation devices (PNDs) rely on two-dimensional (2D) navigation maps to visualize these landmarks in 2D, three-dimensional (3D) in-car navigation systems are emerging. Most of these 3D navigation systems use photorealistic rendering techniques to visualize 3D landmarks. In this visualization scheme, precise geometry models and detailed photorealistic building textures are needed. These systems require that the appearances of these rendered 3D buildings, roads or other objects match those of the real buildings, roads or other objects as much as possible. Thus, when a driver sees the real 3D buildings through the windshield, he or she could do a photorealistic match to recognize the 3D landmark. On one hand, a 2D navigation system visualizes almost no details of our 3D world. On the other hand, a navigation system based on photorealistic 3D maps tries to visualize every detail of our 3D world, which could be unnecessary.
Most data providers (e.g., Tele Atlas) provide only 3D map element data (e.g., 3D landmarks) that are suitable for direct photorealistic rendering. More particularly, most 3D map element data is provided in the form of polygon meshes attached with photorealistic textures. If no modifications are made, these data can only be used for direct photorealistic rendering. Therefore, these data are not suitable for direct nonphotorealistic rendering (NPR). However, NPR has advantages over photorealistic rending in that NPR may present images in a concise way (without unnecessary details) such that the user can easily match the renderings to the real-life views that he observes, and yet only a low level of computational resources is required to produce the NPR renderings.
What is neither disclosed nor suggested by the prior art is a method for presenting NPR renderings of buildings, landmarks and other 3D objects on a navigation map by use of conventional, commercially available 3D map element data that is intended for photorealistic rendering.